The influence of template extraction on the properties of primary amine templated aluminosilicate mesoporous molecular sieves

Abstract

Aluminosilicate mesoporous molecular sieves (Al-MMS) prepared at room temperature using hexadecylamine as template have been subjected to template extraction prior to calcination. Extraction in ethanol alone removes only that part of the template (in neutral form) which is not associated with framework Al while the presence of a cation (Na⁺ or NH4⁺) ensures total template removal. Template extraction has no effect on elemental composition and for dry (non-calcined) samples results in an improvement in structural ordering. The effect of calcination depends on the mode of extraction; samples extracted in ethanol or ethanol/NH4⁺ are structurally stable to calcination and possess surface area and pore volume similar to directly calcined samples while ethanol/Na⁺ extracted samples are relatively unstable and undergo considerable structural degradation resulting in lower surface area and pore volume. Dealumination results from calcination of amine or ammonium ion containing samples while Na containing samples do not undergo any dealumination. The acid content of calcined ethanol and ethanol/NH₄⁺ extracted samples is comparable to that of the directly calcined samples but the extracted samples exhibit higher catalytic activity for the cracking of cumene. Calcined ethanol/Na extracted samples possess very low acidity and exhibit no catalytic activity.

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